Reducing toxic effects of carboplatin using dithioethers

ABSTRACT

To reduce the toxic effect of carboplatin, particularly myelosuppression and emesis, a dithioether having the formula R 1  -(CH 2 ) n  --S--S--(CH 2 ) m  --R 2  (I) wherein: 
     each of R 1  and R 2  individually is SO 3  H or PO 3  H 2  ; and 
     each of m and n is individually 1, 2, 3 or 4; 
     or a pharmaceutically acceptable salt thereof, preferably disodium 2,2&#39;-dithiobis(ethane sulfonate) (dimesna), is administered in combination with carboplatin to a patient, at substantially the same time or sequentially, whereby the dithioether and the carboplatin become co-present in the blood of the patient. Compositions comprising carboplatin and the dithioether are included in the invention.

This application claims benefit of Provisional Application 60/026,430filed Aug. 23, 1996.

FIELD OF THE INVENTION

This invention relates to reducing the toxicity of carboplatin(cis-diammine-1,1-cyclobutanedicarboxylato-platinum II, CBDCA, JM-8 andNSC 241240), using a dithioether as a protective agent.

BACKGROUND OF THE INVENTION

Carboplatin (hereinafter also referred to as "CBDCA" or CBP") is awidely used anticancer drug which is normally used in combination withother anticancer drugs in the treatment of cancers of the lung, head andneck, ovary, esophagus, bladder, testis, and others. One of the mostimportant and common dose limiting toxicities of carboplatin ishematological toxicity. In particular, myelosuppression (depression ofblood elements formed within bone marrow) is often manifested in theform of thrombocytopenia, neutropenia, leukopenia, and various forms ofanemia. The other major carboplatin-induced toxicity isgastro-intestinal (causing nausea and vomiting).

In order for carboplatin to react with certain nucleic acid sequences incellular DNA, it must first undergo chemical conversion to an activespecies by the partial or complete displacement of thecyclobutanedicarboxylato (CBDC) ligands, respectively, by chloride. Thechloro and dichloro species are believed to act against cancer cells byreacting with the imidazole nitrogens on DNA. These chloro species arebelieved to be metabolised in vivo to active hydroxy species.

Carboplatin, unlike cisplatin, is relatively stable in the body. Itscyclobutanedicarboxylato (CBDC) group makes it much less susceptible todisplacement by incoming nucleophiles. It is less active than cisplatintowards DNA. Indeed, it is generally given in combination with otheranti-cancer drugs. Although less prone to cause the nephrotoxicityassociated with cisplatin, it is highly myelotoxic and hasgastrointestinal toxicity. It might at first be thought thatcarboplatin, with its active chloro species, should behave similarly tocisplatin and therefore be further metabolised in the same way. However,this is not so: the body cells most adversely affected bycarboplatin-induced toxicity (bone marrow and GI tract cells) aredifferent from those most adversely affected by cisplatin (kidneycells). Thus, the metabolic species responsible for the toxicity cannotbe the same. Finding a protective agent for carboplatin thereforerepresents a new and separate problem from that presented by cisplatin.

SUMMARY OF THE INVENTION

It has now been found that a dithioether having the formula R₁--(CH₂)_(n) --S--S--(CH₂)_(m) --R₂ (I) wherein:

each of R₁ and R₂ individually is SO₃ H or PO₃ H₂ ; and

each of m and n is individually 1, 2, 3 or 4; or a pharmaceuticallyacceptable salt thereof, is a suitable protective agent for carboplatin.

This invention can be represented in different ways according to localpatent law. Thus, it includes the use of the dithioether in themanufacture of a medicament for administration in combination withcarboplatin to a patient, at substantially the same time orsequentially, whereby the dithioether and the carboplatin becomeco-present in the blood of the patient and the dithioether serves toreduce the toxicity of the carboplatin. It further includes a method oftreating a patient suffering from a cancer susceptible to carboplatintherapy, which comprises administering the dithioether to the patient atthe above-recited time. Also within the invention is a medicament fortreating cancer in combination with carboplatin therapy, comprising thedithioether.

The preferred dithioether is sodium 2,2'-dithiobis(ethanesulfonate),herein abbreviated to dimesna.

The invention is useful in relation to any cancer treatable by a therapyconsisting of or including administration of carboplatin, especially thecancers specifically listed above.

The invention also includes a composition suitable for administration topatients with cancer, comprising carboplatin and a dithioether asdefined above, especially in the form of a sterile injectable solution,preferably of pH 2 to 6.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The carboplatin formulation used in the invention will typically be asolution. It can take any form appropriate to or conventional forformulation of carboplatin. The type of formulation will of coursedepend on the route of administration, which will normally beparenteral, especially intravenous, and preferably by injection. Thepreferred solvent is aqueous, since carboplatin has a water-solubilityof 14 mg/mL. The formulation will normally contain from 0.05 mg/mL up tothe maximum solubility of carboplatin. It may also include mannitol (apreservative) . It may contain other excipient(s) and/or diluent(s).

The carboplatin formulation will normally have a pH of from 2 to 6; aneutral pH of about 7 is much less preferred. Any pharmaceuticallyacceptable acid, including hydrochloric acid, may be used to adjust thepH. However, a formulation which is substantially free of added chlorideions, or, at least, free of chloride ions from added sodium chloride,has been shown to have improved stability. Cisplatin, by contrast, ispreferably formulated in a chloride ion solution, such as isotonic orhypertonic saline for injection.

The dithioether protective agent is formulated separately from thecarboplatin. For oral administration, it may be formulated as a tablet,capsule, caplet, colloidal suspension or solution, or other form whichis easily ingested by the patient. For parenteral administration it ispreferably formulated as a sterile injectable solution, as describedabove. The oral and/or parenteral formulation may be stored as anaqueous solution or as a lyophilized powder suitable for reconstitutionwith water or another solvent.

Hereinafter, the dithioether will be discussed mainly with reference todisodium 2,2'-dithiobis(ethanesulfonate) (dimesna), but the personskilled in the art will readily be able to use the principles of thisinvention in relation to other dithioethers of formula (I), especially acompound of formula (I) in which m and n are from 1 to 3, in the form ofa sodium salt.

The preferred dithioethers are the sulfonates, especially the disodiumsalts thereof, but including the monosodium, monopotassium,sodium-potassium, dipotassium, calcium and magnesium salts of thesulfonate. Further, since it is the dithio group which must provide areactive nucleophile for quenching the reactive species of carboplatinand the sulfonate group confers water-solubility on the molecule, itfollows that the sulfonate group could be replaced by phosphonate. Thus,disodium and tetrasodium 2,2'-dithiobis(ethanephosphonates) are alsopreferred dithioethers for use in the invention.

For the dithioether formulation, the preferred solvent is aqueous, sincethe dithioethers are also water-soluble, e.g. up to 300 mg/mL fordimesna. The concentration of dithioether is normally from 1 mg/mL up tothe maximum solubility. In principle, higher amounts of the dithioetherare usable, e.g. up to 500 mg/mL, although, of course, solubilityproblems may arise. The formulation may contain excipient(s) and/ordiluent(s).

The carboplatin/dithioether combination can be administered to human ornon-human patients as a treatment for various types of cancer, asdescribed in the effectiveness profile for carboplatin. It may beadministered as a "single drug therapy" (carboplatin being the solecytotoxic or anti-cancer therapeutic agent) or in combination with othercytotoxic, anti-cancer or other chemotherapeutic agents.

Typically, the carboplatin and the dithioether formulations will beprepared as for intravenous injection in sterile, single-dosecontainers. Both could be administered orally.

Preferably the dithioether is administered before the carboplatin,especially from 5 minutes to 1 hour before. For dimesna, from 15 to 30minutes before has been found very effective. Administration of thecombination of carboplatin and the dithioether may require adjustmentsin one or both of timing and/or dosage. The goal in the treatment is tomatch the peak in vivo concentration of the dithioether with that of thetoxic metabolites of carboplatin. Although carboplatin reacts slowly invivo to produce the active nucleophilic species which ultimately causedamage in certain cells, especially bone marrow and GI tract cells, ithas been found that at least the greater proportion of the dose ofdithioether should be given before the carboplatin, although it willsometimes be helpful to give the remaining, smaller proportion, of thedose of dithioether after the carboplatin, in order to combat theeffects of slowly-generated or long-lasting active nucleophilic speciesof carboplatin. Carboplatin has a relatively long half-life in the body.Desirability and necessity of additional doses of protective agent isdetermined by carefully monitoring the patient's excretion of platinumto estimate the rate of drug elimination from the body.

The invention includes the possibility of administering at least a partof the dithioether in the form of a composition comprising thecarboplatin and the dithioether components, preferably as an aqueoussolution of pH 2 to 6. Features of preference of such compositions areas recited above for the individual components.

The carboplatin can be administered in any conventional dose. It may bepossible to exceed the conventional dose of carboplatin, as this isfrequently limited by the toxicity problem which the present inventionmitigates. The carboplatin dose will normally be in the range 0.3 to 45mg/kg (a corresponding dose of dithioether would then be from 20 to 2500mg/kg, increasing roughly proportionately with the carboplatin dose). Interms of body surface area, ranges of 100 to 1000 mg/m² of carboplatinand 1000 to 40,000 mg/m² of dithioether are suggested.

Since the toxicity of the protective agent is very low (the parenteraland oral LD₅₀ values for all of the dithioethers of formula I aregenerally higher than that of common table salt, and all are rapidlyeliminated through excretion in the urine), large amounts of theprotective agent may be given either orally or parenterally to provideconstant and safe protection against any residual carboplatin toxicity.Thus, typically the weight ratio of carboplatin to dithioether used inthe therapy is from 6:1 to 1000:1, most especially 25:1 to 700:1.

The following non-limiting Examples illustrate the invention. The vialsreferred to are "amber vials", which protect the carboplatin fromexposure to light. Although Examples 1 to 4 relate to solutions ofcarboplatin and the dithioether together, it will be appreciated thatthey can be formulated separately, with the carboplatin at acidic pH andeach active component at the concentration indicated in the solutions ofthe Examples.

EXAMPLE 1

(a) Preparation of 2,2'-dithiobis(ethanesulfonate) (dimesna)

Disodium 2,2'-dithiobis(ethanesulfonate) was prepared by oxidizing2-mercaptoethanesulfonate in water with an equimolar amount of iodine aspreviously reported by L. Lamaire and M. Reiger, J. Org. Chem. 26,1330-1, (1961). The other sulfonate and phosphonate dithioethers offormula (I) can be prepared analogously.

(b) Stability of dimesna

50 mg of the dimesna thus prepared were dissolved in 1 mL of water andthe pH of the solution adjusted to 1.5, 2.0, 3.0, 4.0, 5.0 and 6.0 byadding in hydrochloric acid in water or the pH adjusted to 8.0 and 9.0by adding 1 N sodium hydroxide in water. The solution was then stirredfor 24 hours at room temperature, the water was removed at reducedpressure and the residue dissolved in spectral grade D₂ O. The protonNMR spectrum gave only peaks corresponding to the starting material.Heating the pH 1.5 solution to 100° C. for 10 minutes gave no change inthe proton NMR spectrum. These data indicate that dimesna is stable inaqueous solution at pH 1.5 to 9.0.

(c) Preparation of a sterile solution of carboplatin and dimesna

Pure hydrochloric acid (99.999%) was added to a sterile, injectable,Lactated Ringer's (LR) solution (US Pharmacopoeia grade), to give a pHin the range 2.0 to 6.0. 1 mg of pure carboplatin/mL of the above LRsolution was added and allowed to completely dissolve by agitation(1500-2500 rpm) at room temperature, for approximately 60 to 90 minutesin the dark. Then, 15 mg of dimesna, prepared above, per mL of solutionwere added and the mixture agitated until complete dissolution occurred.The final pH was adjusted to within the range pH 2.0 to 6.0 by addingfurther pure hydrochloric acid. The solution was sterilized byfiltration through a sterile 0.2 micrometre filter (obtained from VWRScientific) and stored in sterile injection vials. Each vial containedapproximately 0.9 mg of carboplatin and 14.3 mg of dimesna per mL ofsolution.

EXAMPLE 2

To a sterile injectable aqueous solution of LR solution(USP grade) wereadded 15 mg of dimesna/mL of solution. The dimesna was allowed todissolve completely by agitation (1500-2500 rpm) at room temperature,for 5-10 minutes. The pH of the solution was adjusted to within therange 2.0 to 6.0 by adding pure (99.999%) hydrochloric acid. 1 mg/mL ofdimesna solution of pure (98.0%) carboplatin was added and the mixtureagitated in the dark until complete dissolution occurred. The remainingsteps were as in Example 1 (c), giving a solution of the sameapproximate composition. Each vial contained approximately 1.0 mg ofcarboplatin and 14.3 mg of dimesna per mL of injection solution.

EXAMPLE 3

Example 1(c) was repeated except that 0.5 mg/rnL of carboplatin and 30mg/mL of dimesna were used. Each vial contained 0.5 mg of carboplatinand 12.9 mg of dimesna per mL of injection solution.

EXAMPLE 4

Example 1(c) was repeated except that pure mannitol (99+% purity, fromAldrich Chemical Company) was dissolved in the LR solution, to give aconcentration of 1.0% w/v mannitol, and also that 30 mg/mL of dimesnawere used. Each vial contained approximately 1.0 mg of carboplatin and12.9 mg of dimesna per mL of injection solution.

EXAMPLE 5

Use of Dimesna to Reduce Carboplatin Toxicity

Experiments were performed to determine the efficacy of dimesna inreducing the toxicity of carboplatin in adult beagle dogs. Toxic effectswere tested at varying dose levels of carboplatin, with or withoutadministration of dimesna. The carboplatin used was an aqueous solutionfrom vials of "Paraplatin" (Bristol Myers Squibb) and injected i.v. by aslow drip over 5 to 10 minutes. Lyophilised dimesna was reconstituted inwater and injected i.v. 30 minutes before the carboplatin.

Table 1 gives the dosing schedule followed in the experiments, with twoanimals, one male and one female in each group.

                  TABLE 1                                                         ______________________________________                                                                 Carboplatin                                          Group                 Dimesna (mg/kg)                                         ______________________________________                                                                 (mg/kg)                                              1            0           45                                                   2                                       45                                    3                                          30                                 4                                       30                                    5                                          20                                 6                                       20                                    7                                          13                                 8                                       13                                    9                                       0                                     ______________________________________                                    

The animals were closely observed after the dose was administered, andeuthanized on day 30 for tissue necropsy. Tissues were trimmed,processed, and stained slides were prepared of the following: thymus,heart, lung, stomach, duodenum, jejunum, colon, pancreas, liver, kidney,urinary bladder, testis, ovary, spleen, mesenteric and mandibular lymphnodes, bone marrow, ischiatic nerve, and all gross lesions. Lesionsfound were graded from one to five based upon severity.

Results

Three dogs, the two from control Group 1 which received only a 45 mg/kgdose of carboplatin, and the female from control Group 3 (30 mg/kgcarboplatin only), died or were sacrificed because of their moribundcondition prior to day 30. Most of the other dogs from control Groups 3,5 and 7 exhibited moderate to severe cellular depletion of femoral bonemarrow, moderate to severe lymphoid depletion of the thymus, and othermicroscopic lesions, particularly in the gastrointestinal tract. Thedogs from the Groups 2, 4, 6 and 8, which were given dismesna, allsurvived for the duration of the experiment. Dogs from Groups 4, 6 and 8showed no cellular depletion of the femoral bone marrow or lymphoiddepletion in the thymus. The dogs from Group 2, which received inessence, a lethal dose of carboplatin, both survived and exhibited onlymild lymphoid depletion, with no evident cellular depletion of bonemarrow. Group 9 control dogs which received only dimesna showed nophysiological changes.

What is claimed is:
 1. A method for reducing the unwanted toxicity ofcarboplatin, said method comprising administering to a patient aneffective amount of a dithioether having the formula R₁ --(CH₂)_(n)--S--S--(CH₂)_(m) --R₂ (I) wherein:each of R₁ and R₂ individually is SO₃H or PO₃ H₂ ; and each of m and n is individually 1, 2, 3 or 4; or apharmaceutically acceptable salt thereof and an effective amount ofcarboplatin, at substantially the same time or in a sequential manner.2. The method of use according to claim 1, wherein the dithioether isadministered to the patient prior to the administration of carboplatin.3. The method of use according to claim 2, wherein the dithioether isadministered at a time from 5 minutes prior to 1 hour prior to theadministration of carboplatin.
 4. The method of use according to claim1, 2 or 3, wherein the dithioether and the carboplatin are administeredeither both intravenously or both orally.
 5. The method of use accordingto claim 1, 2, 3 or 4, wherein the weight ratio of dithioether tocarboplatin administered is from 25:1 to 700:1.
 6. The method of useaccording to claim 1, 2, 3, 4 or 5, wherein the dithioether is acompound of formula (I) in which m and n are from 1 to 3, in the form ofa sodium salt.
 7. The method of use according to claim 6, wherein thedithioether is dimesna, being the compound of formula (I) in which m andn are 2 and R₁ and R₂ are SO₃ H, in the form of the disodium salt. 8.The method of use according to claim 7, wherein the dimesna isadministered from 15 to 30 minutes before the carboplatin.
 9. Acomposition suitable for administration to patients with cancer,comprising an effective amount of carboplatin and a dithioether havingthe formal R1--(CH2)n--S--S--(CH2)m--R2 (I) wherein: each of R1 and R2individually is SO3H or PO3H2; and each of m and n is individually 1, 2,3 or 4; or a pharmaceutically acceptable salt thereof.
 10. A compositionaccording to claim 9, in the form of a sterile injectable aqueoussolution or suspension of pH 2 to
 6. 11. A composition according toclaim 10, wherein the weight ratio of dithioether to carboplatin is from25:1 to 700:1.